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Generating value from wood waste

Alan Sherrard

Heat & Power

October 5, 2017

Bioenergy International joined a World Bioenergy Association (WBA) field trip to Miyazawa Wood Working Industry Co., Ltd organised as part of WBA’s mission to Japan earlier this year. A visit that provided a first-hand glimpse into how a small-scale biomass power plant can generate value from waste wood and resuscitate a local forest-based economy out of decline.

Participants in World Bioenergy Association’s (WBA) field trip to Miyazawa Wood Working Industry Co (MWWI).

Tucked in the forested foothills of Mount Iizuna, is Miyazawa Wood Working Industry Co., Ltd, (MWWI) a family run company specialised in wood recycling. Located in the Hokushin district about a 20-minute drive from Nagano city, host city of the 1998 Winter Olympics, the site is the location of a biomass power plant and a pelleting plant.

Wood for energy

The Hokuskin area in Nagano Prefecture is densely forested, predominately with low-quality Japanese cedar (Cryptomeria japonica) or sugi as it is called in Japan.

Stockpiles of unused pulpwood, predominately Japanese cedar (Cryptomeria japonica), along with Japanese red pine (Pinus densiflora) and with some hardwood species on the upper logyard.

Pulpwood has been the traditional product, however, a decline in demand from the pulp industry has meant that volumes of unused wood were beginning to accumulate and forestry jobs harder to come by.

In 2003, seven companies in the Hokushin area, including MWWI, a forestry contractor, a waste service company, and a construction company, founded the ”Nagano Forest Resources Use Cooperative Business Association” with the goal of developing biomass power generation as a new use for the unused pulpwood.

Grinders and chippers galore – parked on the MWWI site, a well used Vermeer and a Ryokusan (Komptech) chipper both tracked for use in forest operations.

Through the combined efforts within the cooperative, the biomass plant has full control, running its own forest harvesting crews, haulage and waste wood collection fleet, fuel preparation with a fleet of grinders and chippers, operations and maintenance (O&M) of the plant and electricity sales.

Wheeled Doppstadt’s are used for onsite fuel preparation, an AK 510 high-speed grinder and a DH 810 disc chipper.

Infrastructure, location, location

Compared to many places, land in Japan is at a premium and being sited on a steep slope is not without challenges. However, it was chosen on account of having few neighbours and, more importantly, both the road and electrical infrastructure including high-voltage cables were already ”well-organised” – a fringe benefit of Nagano hosting the Winter Olympics in 1998. The availability of the infrastructure also meant a reduced upfront investment cost.

A view over the cooling towers from the upper logyard reveals the split-level construction approach. The entire facility is sited snug into the hillside with flue stacks and cooling towers at tree level.

Almost identical setup

The first unit, at 1.3 MWe capacity was commissioned in 2005 under the RPS scheme before being reassigned in 2013 under the FIT scheme that was introduced in 2012. Of the JPY 750 million (≈ US$ 6.79 million) investment, JPY 290 million (≈ US$ 2.62 million) was publicly subsidized by Nagano Prefecture for FY2003 under the Nagano Prefecture Local Resources Supply System Project.

The second slightly larger unit at 1.5 MWe capacity was built adjacent to the first one and commissioned in 2014 under the Feed-in Tariff (FIT) scheme. Of the JPY 920 million (≈ US$ 8.32 million) investment JPY 250 million (≈ US$ 2.26 million) was publicly subsidized, again by Nagano Prefecture for FY2013 under the Nagano Prefecture Local Resources Supply System Project.

(Left) The lower yard is also the receiving terminal for waste wood and roundwood. Although the two stoker grate boilers (right) can handle either or fuel, the two streams are kept entirely separate on account of the different feed-in tariff (FIT) rates for each respective unit. Each boiler unit has its own ancillaries thus the plant is essentially two almost identical biomass power places built side-by-side.

Both plants have high automation, use the same make of stoker grate steam boilers and have separate but identical ancillary equipment; fuel infeed line, flue gas treatment, steam turbine and generator, cooling towers, ash removal and granulation, condensate and water treatment. This dual compatibility enables parts sharing and effective maintenance.

Policy-driven fuels

On an annual basis, the two units combined use around 40 000 tonnes of chipped/crushed material. Both boilers can handle materials with up to 55 percent moisture content so no pre-drying of green material takes place. The ash is processed into granulates and used as a filler in construction.

Up until when unit 2 was commissioned in 2014, unit 1 used a mixed of 70 percent “recycled wood” such construction and demolition (C&D) wood, packaging and 30 percent unused pulpwood. Once unit 2 started in 2014, the FIT scheme with its biomass source tariff banding had already been introduced.

Busy receiving yard with four trucks in, three from the own haulage fleet with unused wood logs and a fourth (far left) a third party delivery of waste wood. In the background is the “clean” woodchip storage shed. A weighbridge system is used, whereby trucks are weighed on entrance and again after unloading, to determine the amount of fuel coming in.

“Satochi-satoyama” pellets

MWWI is able to cover 60 to 70 percent of the fuel demand for the plant with the balance purchased from national, public and private forests. As fuel costs represent the single largest item the company is exploring additional biomass sources to reduce fuel costs and increase self-sufficiency.

A blend of “satochi-satoyama” residues comprising of grass and reeds blended with cedar bark on the dryer infeed conveyor. (Right) the final pellet product. The pelleting plant has a “guesstimated” annual capacity of 5 000 to 6 000 tonnes.

By investing in a small pelleting line complete with a dryer that uses exhaust heat from the power plant, the company can provide a gate-fee disposal service for this type of green waste, typically grass and brush. This is then blended with wood bark, dried and pelletized to produce fuel for the plant.

“Satochi-satoyama” are tracts of rural land located between cities and wilderness, comprising of villages, secondary and planted forests that surround villages, farmland, ponds and similar geographical areas that are maintained by local residents. The solution lies right outside the doorstep with agri-based biomass from “satochi-satoyama” maintenance.

This article was first published in Bioenergy International no. 5-2017. Note that as a magazine subscriber you get access to the e-magazine and articles like this before the print edition reaches your desk!